Ch2-notes

Ch2-notes - Ventilation 1. How can you measure the volume...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Ventilation 1. How can you measure the volume of a subject? 2. How do you measure lung volume? 3. What is the difference between anatomical and physiological dead space? Archimedes Principle If an object has uniform density W= ρ *V where W=weight =density and V=volume. Weight while submerged Ws=W- ρ water *V V=(W-Ws)/ ρ water Or ρ =W/V This forms the basis of the “dunking” method of measuring body density which correlates better than weight with fitness level. The main correction needed is for lung volume V lung which has 0 density. ρ corrected =W/(V-V lung ) The correction for lung volume usually is made using estimates based on prediction formulas based on sex,age,and height values. However, it really should be measured for each individual. Measurement of Lung Volume
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The standard (clinical) method of measuring changes in lung volume is with a spirometer. This is a direct volume displacement device where a subject inspires from or expires into the unit for the measurement with a noseclip applied and a mouthpiece used. Pictured below is a water sealed spirometer which was once widely used but is now obsolete due to contamination problems. The picture actually shows a subject hooked up to measure the relaxation pressure at different lung volumes. Note the water manometer for pressure measurement and closed respiratory valve just below the spirometer. This will be covered later in the mechanics section. The replacement of the water seal with a silastic membrane led to the dry rolling seal spirometer shown below.
Background image of page 2
Versions of this spirometer is still used especially in hospitals. The inside of the “dry” spirometer in use is still quite wet with breath condensation. These spirometers are considered the “gold standard” of breath volume measurements. A more accurate method does not exist and many in common use may be more compact but cannot be relied on for more than 10 % accuracy at best. Spirometer measurements are primarily used to diagnose lung disease. Since breathing problems mainly affect the very young or old most young adults (except for asthmatics) have never undergone a pulmonary function test. Since this measurement is to be compared to a normal value, the first issue concerns the units. BTPS and STPD volume units BTPS(Body temperature, Pressure saturated with water vapor, ambient barometric pressure) This conditions corresponds to the lungs at usually the normal 37 deg C. when a spirometer is used to measure a respired volume the condition corresponds to spirometer temperature Ts (usually about 20 deg C) and ambient barometric pressure B(760 mm Hg in LA) and the gas is saturated with water vapor. BTPS units require the following calculation: nR=(760-17.5)*Vspirom/(273+20)=(760-47)*VBTPS/(273+37) VBTPS=1.10*Vspirom
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/15/2012 for the course BME 403 taught by Professor Yamashiro during the Spring '07 term at USC.

Page1 / 8

Ch2-notes - Ventilation 1. How can you measure the volume...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online